This is the third renewal of a program whose long term objective is to develop improved diagnostic techniques and provide a more rational foundation for therapeutic interventions in the hearing impaired, of all ages. The specific focus in this renewal is on the development of new methods for quantifying the contribution of non-linear mechanisms to the processing of auditory information. It is specifically hypothesized that non-linear mechanisms are important contributors to the operation of the auditory system and that an improved understanding of the sensorineural impaired individual will require the detection and quantification of these non-linear processes. Therefore a series of descriptive measurements are proposed in which specific non-linear phenomena are quantified in normal hearing, newborn and hearing impaired adults. It is hypothesized that the most sensitive and specific measure of sensor-neural impairment will be these non-linear processes. It is further hypothesized that these non-linear processes will arise later and mature more slowly than linear processes. Digital signal processing principles are used to develop novel measurement procedures and to create a more general framework from which both linear and nonlinear activity can be analyzed. This framework should also accommodate both frequency and time domain abnormalities. Thus, the experiments proposed herein are theoretical, descriptive and hypothesis driven. Of special note is the fact that all of the methods described herein can be used in patients of all ages. The successful completion of these goals will have a significant impact on the practice of diagnostic audiology and otolaryngology in addition to advancing our understanding of the mechanisms involved in human auditory pathology.